feat: add yew-link crate for unified SSR/CSR data fetching

[Madoshakalaka]

Description

Closes #2649, whose lower-level half includinguse_prepared_state and use_transitive_state is already shipped

This PR implements the higher-level half of #2649: a yew-link crate that unifies SSR, hydration, and client-side data fetching behind a single hook.

The mentioned lower-level hooks already carry server-computed state to the client during hydration. But after that initial page load, client-side navigation requires a completely separate fetch path. This means every data-dependent component needs two code paths stitched together manually. yew-link closes this gap.

Implimented new crates proposed in the pr: yew-link and yew-link-macro

Overhauled ssr_router example, rewired to use yew-link instead of generating content inline. Demonstrates #[linked_state], LinkProvider, use_linked_state, Resolver::register_linked, and the axum handler, with full SSR-to-hydration state transfer and client-side nav fetching.

See the new website changes to understand the usage pattern

Comparison with Bounce's Query API

@futursolo's Bounce, whose Query API and use_prepared_query hook do overlapping but not identical work

yew-link does better on code isolation as its #[linked_state] strips resolve() from WASM and Query::query() body is always compiled into WASM.

yew-link also provides better utility by its built-in linked_state_handler for axum.

After #4013 merges

#4013 replaces the hand-maintained feature-soundness scripts with cargo-hack --feature-powerset. Once it lands:

• Add yew-link to the cargo hack clippy -p ... list in .github/workflows/clippy.yml and packages/yew/Makefile.toml so its feature combinations (ssr, hydration, axum) are covered automatically.
• Add yew-link,yew-link-macro to --exclude-features if any of their features shouldn't participate in the powerset (will check).

Remaining TODOs (future PRs)

• Cache invalidation / refresh, expose a .refresh() method or TTL-based expiry.
• Non-suspending variant, a use_linked_state_value that returns Loading | Ok | Err instead of suspending.
• Mutations, write-side counterpart to use_linked_state.
• Deduplication, multiple components requesting the same (T, input) concurrently should share a single in-flight request.
• Tests, unit tests for the hook (SSR + hydration + CSR paths) and integration tests for the axum handler.

Basically everything else Bounce does correctly

I'm not sure how cargo release in our .github/workflows/publish.yml handles the two added new crates, but that's a matter for the future when when publish yew-link with yew 0.23

Checklist

• I have reviewed my own code
• I have added tests

I have to think about tests.
I manually tested the uphauled ssr_example and paid attention to the network requests. The claims hold well: directly visiting a post by its url receives a server-rendered page. In-app navigation goes through fetch.

E2e testing directly on the example might be a good idea, which requires resolving #196 first.

[github-actions]

Visit the preview URL for this PR (updated for commit 5c337a4):

https://yew-rs--pr4027-yew-link-sylkdib6.web.app

_{(expires Sun, 08 Mar 2026 05:38:26 GMT)}

_{🔥 via Firebase Hosting GitHub Action 🌎}

[github-actions]

Benchmark - SSR

Yew Master

Details

Benchmark	Round	Min (ms)	Max (ms)	Mean (ms)	Standard Deviation
Baseline	10	310.749	313.064	311.293	0.672
Hello World	10	467.443	491.807	474.039	9.395
Function Router	10	31374.284	31806.908	31603.390	158.553
Concurrent Task	10	1006.226	1009.943	1007.428	1.018
Many Providers	10	1066.089	1127.129	1098.929	16.895

Pull Request

Details

Benchmark	Round	Min (ms)	Max (ms)	Mean (ms)	Standard Deviation
Baseline	10	310.847	317.339	311.678	1.996
Hello World	10	468.149	473.579	471.135	1.858
Function Router	10	31353.471	31849.147	31669.864	156.539
Concurrent Task	10	1004.796	1007.833	1006.725	0.906
Many Providers	10	1097.205	1128.673	1107.454	8.513

[github-actions]

Size Comparison

Details

examples	master (KB)	pull request (KB)	diff (KB)	diff (%)
async_clock	100.196	100.196	0	0.000%
boids	168.080	168.080	0	0.000%
communication_child_to_parent	93.471	93.471	0	0.000%
communication_grandchild_with_grandparent	105.247	105.247	0	0.000%
communication_grandparent_to_grandchild	101.604	101.604	0	0.000%
communication_parent_to_child	90.897	90.897	0	0.000%
contexts	105.151	105.151	0	0.000%
counter	86.281	86.281	0	0.000%
counter_functional	88.274	88.274	0	0.000%
dyn_create_destroy_apps	90.319	90.319	0	0.000%
file_upload	99.342	99.342	0	0.000%
function_delayed_input	94.374	94.374	0	0.000%
function_memory_game	172.940	172.940	0	0.000%
function_router	405.773	405.773	0	0.000%
function_todomvc	164.160	164.160	0	0.000%
futures	235.158	235.158	0	0.000%
game_of_life	104.717	104.717	0	0.000%
immutable	255.871	255.871	0	0.000%
inner_html	80.802	80.802	0	0.000%
js_callback	109.380	109.380	0	0.000%
keyed_list	179.727	179.727	0	0.000%
mount_point	84.146	84.146	0	0.000%
nested_list	113.059	113.059	0	0.000%
node_refs	91.524	91.524	0	0.000%
password_strength	1729.151	1729.151	0	0.000%
portals	93.036	93.036	0	0.000%
router	376.334	376.334	0	0.000%
suspense	113.455	113.455	0	0.000%
timer	88.633	88.633	0	0.000%
timer_functional	98.880	98.880	0	0.000%
todomvc	142.087	142.087	0	0.000%
two_apps	86.146	86.146	0	0.000%
web_worker_fib	136.238	136.238	0	0.000%
web_worker_prime	187.468	187.468	0	0.000%
webgl	83.225	83.225	0	0.000%

✅ None of the examples has changed their size significantly.